1. Field of the Invention
The present invention relates to valves and pumps. In another aspect, the present invention relates to ball and seat valves, and to pumps utilizing said valves. In even another aspect, the present invention relates to ball and seat valves utilizing a piston mechanism to unseat the ball from the seat, and to downhole pumps utilizing said valves.
2. Description of the Related Art
In the production of hydrocarbons from subterranean formations, it is desirable that the pressure of the formation "produce" or force the hydrocarbons to the surface. Unfortunately, sometimes formation pressure may be initially too low to produce the formation, or may decline to that point as hydrocarbons are produced from a formation. Resort must then be made to the use of a pump to produce the formation.
Most commonly in petroleum production technology, producing wells utilize a so called "sucker rod" to lift oil from subterranean formations to the surface of the earth. Sucker rod pumps are generally either a rod pump or a tubing pump. Tubing pumps are constructed such that the barrel assembly is an integral part of the tubing string and such that the plunger assembly is part of the rod string. Rod pumps, however, are of the stationary barrel traveling plunger type, wherein the barrel assembly is wedged into the seating nipple at the bottom of the tubing, thus providing a seal point.
In general a sucker rod pump is a reciprocating pump which is normally secured to the lowermost end of the sucker rod string, which extends longitudinally through the well bore from a reciprocating device at the surface of the ground. The reciprocating device at the surface is usually a horsehead type apparatus and alternatively raises and lowers a string of sucker rods in the well bore.
The sucker rod pump itself generally includes a housing through which a piston is reciprocated by the sucker rod linkage. In its simplest form, the pump usually includes a number of ball and seat valves with one such valve in the piston and another at the inlet port of the housing. On the upstroke of the plunger, the ball in the inlet port valve ("standing valve") is drawn away from its seat and the ball of the outlet port valve ("traveling valve") is forced over its seat to draw fluid from below the seating nipple and into the housing. On the piston's downstroke, the ball in the standing valve is forced into its seat and the ball in the traveling valve moves away from its seat to allow the piston to move downwardly through the fluid contained in the housing. On the subsequent upstroke, the closing of the traveling valve forces the fluid above the piston, out of the housing through the outlet ports and into the tubing above the pump and simultaneously fills the housing below the piston with fluid. Repetition of this cycle eventually fills the tubing string and causes the fluid to flow to the surface.
One problem encountered by sucker rod pumps is caused by the wear of the ball and seat valves. The fluid produced from many geological formations contains minute, abrasive particles, such as sand, which lodge between the ball and seat and wear away the valve components. Over a period of time, the sealing efficiency of the valves is reduced to such an extent that the pump must be removed and repaired or replaced. In some wells, where the production fluid is particularly sandy or corrosive, these pumps must be replaced at frequent intervals. It is, of course, evident that removing and repairing or replacing a pump, and the associated losses of lost production time during the repair or replacement process, can be significant expense factors.
Another problem associated with such conventional ball and valve sub-surface oilfield pumps is generally known as "gas locking". In such pumps, the fluid head pressure in the tubing string is held by the traveling valve, on the upstroke of the piston, and by the lower standing valve on the downstroke of the piston. The down stroke of the traveling valve builds up pressure on the fluid between the traveling valve and the standing valve which causes the traveling valve to open to allow fluid to pass above the traveling valve. However, in a well producing both oil and gas, the chamber between the traveling valve and the standing valve, frequently fills with gas, and due to the compressibility of gas, the downstroke of the traveling valve may not build up sufficient pressure in the chamber below the traveling valve to act upwardly on the ball of the traveling valve to overcome the immense pressure of the fluid column above the traveling valve which acts downwardly on the ball of the traveling valve, resulting in the ball of the traveling valve remaining in the closed seated position during the downstroke. Thus, the gas between the standing valve and the traveling valve merely compresses and expands with each stroke of the pump, producing the operational failure of the pump known as "gas locking". This condition may remedy itself after a short time or may continue indefinitely.
Even another problem associated with such conventional ball and valve sub-surface oilfield pumps is generally known as "fluid pounding". This fluid pounding occurs when the pump does not fill completely with liquid during the upstroke, resulting in the formation of a low pressure gas cap in the top of the pump chamber between the traveling valve and the standing valve. During the subsequent downstroke the traveling valve stays closed until it impacts the fluid.
There has been a long felt need to solve the above described problems associated with such conventional ball and valve sub-surface oilfield pumps, and the art is replete with attempts to solve one or more of the above problems.
U.S. Pat. No. 1,585,544, issued May 18, 1926 to Hubbard, discusses the problem of "air hammering", and suggests the use of a rod mounted on the standing valve which impacts the ball of the traveling valve as the traveling valve is moved toward the standing valve. However, given the expansion and contraction of the sucker rods, the traveling valve may not reach the rod, or may extend past the rod, damaging the valve.
U.S. Pat. No. 4,691,735, issued Sep. 8, 1987 to Horton, discloses a traveling valve for an oil well pump, which includes a piston below the traveling valve which lifts the traveling valve ball above the traveling valve seat. On the downstroke, pressure builds up between the standing valve and the piston, to force the piston upward to lift the ball. However, since the piston cross-sectional area affected by the pressure between the standing valve and the piston is equal to the cross-sectional area of the traveling valve seat, no mechanical advantange is provided by the arrangement of Horton. Thus, Horton suffers from "gas locking" to the same extent as conventional traveling valves. Additionally, the Horton traveling valve and the rod assembly are not mounted below the bottom of the plunger, and thus must be made of materials strong enough to withstand the rigors of operation of the pump.
U.S. Pat. No. 4,781,547, issued Nov. 1, 1988 to Madden, discloses a pushrod assembly mounted below the traveling valve, which pushrod is alternatively moved from an extended into a retracted position each upstroke and downstroke of the pump. The free terminal end of the pushrod is arranged to engage the traveling valve ball as the pump commences the downstroke. However, since the bottom of the pushrod includes several channels, pressure does not build up between the pushrod and the standing valve during the downstroke. Rather, during the downstroke liquid is forced through the channels in the bottom of the pushrod. Movement of the pushrod is affected by inertia, pressure differential of the liquid flow through the channels, and friction between the pushrod and the pump barrel.
Therefore, there is a need in the art for an improved downhole reciprocating pump.
There is another need in the art for an improved apparatus for moving the traveling valve ball during the downstroke of a downhole reciprocating pump.
These and other needs in the art will become apparent to those of skill in the art upon review of this patent specification, claims and drawings.